Two major considerations of barrier performance relevant to polyethylene terephthalate ("PET") containers are: the ability to retain carbon dioxide within the bottle, specifically for carbonated beverages such as colas and beers; and the ability to minimize oxygen ingress through the container, specifically oxygen sensitive products such as beer and wine. To this end, manufacturers of PET containers have sought various methods to produce PET containers which increase these two attributes.
One method to obtain these attributes in PET containers is to produce multi-layered bottles composed of at least one layer of an ethylene vinyl alcohol, nylon or poly(ethylene 2,6-naphthalene dicarboxylate) ("PEN") material. An example of such is disclosed in Peece et al, U.S. Pat. No. 5,084,352, for Multilayered Barrier Structures For Packaging. Another method is manufacture a container from a PET/PEN blend material. Still another method is to coat a PET bottle with a polyvinylidene-chloride ("PVDC") film.
The packaging industry has previously produced multi-layered packaging materials consisting of at least one skeletal layer which is composed of a blend of a polymer material and an inorganic filler material. Most of these packaging materials have included the inorganic filler to increase the light-shielding and thermal insulating properties of the package, with a few including the inorganic fillers for their ability to enhance the mechanical properties of the package. In practicing such inventions, the particular size of the inorganic filler particles has not been addressed since these inventions were only seeking to capture the bulk properties of these inorganic fillers for use in their packaging. An example of such is disclosed in Rosen, U.S. Pat. No. 5,234,763, for a Packaging Material And Also Use Of The Material For The Manufacture of Containers. In Rosen, the inorganic fillers are chalk, talc, lime, mica or clay with the preferred filler being chalk.
A recent trend in many fields is to blend polymer materials with particles of a modified clay mineral with very high aspect ratios. An aspect ratio is the ratio of a particular object's width to its thickness. The nanosize particles of clay usually have a width of several microns while the thickness is in the nanometers, hence the designation "nanosize particles." Much of the work in this area has focused on producing a composite material which increases the mechanical strength and heat resistance of the polymer material. One such example is Deguchi et al, U.S. Pat. No. 5,102,948, for a Polyamide Composite Material And Method For Preparing The Same. An object of Deguchi et al is to provide a polyamide composite which possesses the properties of increased mechanical strength and heat resistance, but also has an improved dye-affinity and whitening resistance. The focus of this packaging trend has been to increase the mechanical strength and heat resistance of the polymeric material. This has resulted in the industry attempting to further increase the weight percentage of inorganic matter while maintaining the polymeric nature of the material.
The foregoing patents fail to address the need for developing a container which has a greater impermeability to the ingress and egress of gases without entirely changing the polymeric nature of the material.